Analysis on the variability of inflows into the Miyun Reservoir was performed at both Xiahui(Chaohe River) and Zhangjiafen(Baihe River) stations and the relationships between the flow volumes and precipitation and land use change were addressed.Based on inflow variability analysis,daily pulse number and mean pulse duration were statistically discussed for the estimation of various stream flow thresholds.The results show that the inflows decreased and exhibited less temporal variability at both Xiahui and Zhangjiafen stations during 2002-2006, comparing to those in the 1980s.The variability of the stream flows was mainly affected by precipitation.The increase of grassland area might reduce the inflow velocity,and the decrease of forest increased the high threshold volumes and at the same time could reduce total flow volume.However,land use change had only little contribution to stream flow variations,owing to only insignificant change was detecte during this time period.